U.S. patent number 6,195,119 [Application Number 09/004,264] was granted by the patent office on 2001-02-27 for digitally measuring scopes using a high resolution encoder.
This patent grant is currently assigned to Olympus America, Inc.. Invention is credited to James G. Costello, Andreas E. Dianna.
United States Patent |
6,195,119 |
Dianna , et al. |
February 27, 2001 |
Digitally measuring scopes using a high resolution encoder
Abstract
A system for determining a dimension of a detail including an
optical scope for producing an image of the detail, an image
scaling device for providing a scaled image size, and a processor.
The system also includes a video camera which is either within the
optical scope or external to the optical scope. The optical scope
includes a focusing device for adjusting a focal position of the
image of the detail and a device for providing a focus position
signal based a position of the focusing device. If the system
includes an external video camera, the optical scope also includes
a viewer for passing the image of the detail to a plane outside of
the optical scope. The video camera optically is coupled with the
viewer of the optical scope or with the image of the detail and
produces a video signal of the detail from the image of the detail.
The processor converts the focus position signal into an object
distance signal, or a magnification signal, or both, and determines
the dimension of the detail based on the scaled image size and
based on the object distance signal, or the magnification signal,
or both.
Inventors: |
Dianna; Andreas E. (Walnut
Port, PA), Costello; James G. (Huntington, NY) |
Assignee: |
Olympus America, Inc.
(Melville, NY)
|
Family
ID: |
27003023 |
Appl.
No.: |
09/004,264 |
Filed: |
January 8, 1998 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
502984 |
Jul 17, 1995 |
5801762 |
|
|
|
365636 |
Dec 28, 1994 |
5573492 |
|
|
|
Current U.S.
Class: |
348/65 |
Current CPC
Class: |
A61B
5/1076 (20130101); G01B 11/02 (20130101); H04N
2005/2255 (20130101) |
Current International
Class: |
A61B
5/107 (20060101); G01B 11/02 (20060101); H04N
007/18 () |
Field of
Search: |
;348/65,348,357
;385/117-118 ;356/241 ;359/367,642 ;607/1 ;600/163,167-168 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Le; Vu
Attorney, Agent or Firm: Kenyon & Kenyon
Parent Case Text
CONTINUATION APPLICATION INFORMATION
This application is a continuation of U.S. patent application Ser.
No. 08/502,984, filed Jul. 17, 1995, now U.S. Pat. No. 5,801,762,
which is a continuation-in-part of U.S. patent application Ser. No.
08/365,636, filed Dec. 28, 1994, now U.S. Pat. No. 5,573,492.
Claims
What is claimed is:
1. A system for determining a dimension of a feature, the system
comprising:
a) an optical scope for gathering an image of the feature, the
optical scope including
i) a focusing device for adjusting a focal position of the image of
the feature,
ii) a device for detecting a position of the focusing device and
for providing a focus position signal based on the position of the
focusing device, and
iii) an image-to-video converter for producing a video signal of
the feature from the image of the feature having its focal position
adjusted by the focusing device;
b) an image scaling device for providing a scaled image size;
and
c) a processor, the processor
i) converting the focus position signal into at least one of an
object distance signal and a magnification signal, and
ii) determining the dimension of the feature based on the scaled
image size and based on the at least one of the object distance
signal and the magnification signal, wherein the dimension of the
feature includes at least one of a depth and height of the
feature.
2. The system of claim 1, wherein the processor includes:
i) a converter for converting the focus position into an object
distance signal; and
ii) means for determining the dimension of the feature by
determining the difference between a first object distance signal
and a second object distance signal.
3. A system for determining a dimension of a feature, the system
comprising:
a) an optical scope for producing an image of the feature, the
optical scope including
i) a focusing device for adjusting a focal position of the image of
the feature,
ii) a viewer for passing the image of the feature to a plane
outside of the optical scope, and
iii) a device for detecting a position of the focusing device and
for providing a focus position signal based on the position of the
focusing device;
b) a video camera optically coupled with the viewer of the optical
scope and producing a video signal of the feature from the image of
the feature;
c) an image scaling device for providing a scaled image size;
and
d) a processor, the processor
i) a converting the focus position signal into at least one of an
object distance signal and a magnification signal, and
ii) determining the dimension of the feature based on the scaled
image size and based on the at least one of the object distance
signal and the magnification signal, wherein the dimension of the
feature includes at least one of a depth and height of the
feature.
4. The system of claim 3, wherein the processor includes:
i) a converter for converting the focus position into an object
distance signal; and
ii) means for determining the dimension of the feature by
determining the difference between a first object distance signal
and a second object distance signal.
5. A system for determining a dimension of a feature, the system
comprising:
a) an optical scope for gathering an image of the feature, the
optical scope including
i) a focusing device for adjusting a focal position of the image of
the feature, and
ii) a device for detecting a position of the focusing device and
for providing a focus position signal based on the position of the
focusing device;
b) a processor, the processor
i) converting the focus position signal into an object distance
signal, and
ii) determining a dimension of the feature based on the object
distance signal.
6. The system of claim 5, wherein the dimension of the feature
includes at least one of a depth and height of the feature.
7. The system of claim 6, wherein the processor includes:
i) a converter for converting the focus position into an object
distance signal; and
ii) means for determining the dimension of the feature by
determining the difference between a first object distance signal
and a second object distance signal.
Description
BACKGROUND INFORMATION
The present invention concerns an arrangement, which includes a
scope, such as a rigid borescope, a flexible fiberscope, or a
videoscope for example, for accurately measuring observed objects,
object details, and object defects. The arrangement of the present
invention is more accurate than known systems, yet is simple to
use.
Scopes, such as flexible videoscopes and fiberscopes have been used
to observe the interior of the body during diagnostic procedures or
surgery. Scopes, such as rigid borescopes, have been used to
observe and inspect manufactured parts otherwise inaccessible to
the eye. Although such scopes have an almost limitless number of
applications, the following example illustrates their value.
A gas turbine engine includes a series of compressor and turbine
blades, any one of which may become damaged. Although the first and
last stage compressor/turbine blades of a gas turbine engine can be
inspected directly, other intermediate stage compressor/turbine
blades cannot be directly inspected. In the past, to inspect these
intermediate stage compressor/turbine blades, the engine had to be
disassembled until the intermediate stage compressor/turbine blade
could be directly inspected. However, more recent gas turbine
engines are provided with apertures (or borescope ports) provided
at critical areas. These borescope ports permit the intermediate
stage blades to be inspected using a borescope.
The borescope includes a long, thin, insertion tube having a lens
system at its distal end and a viewing means at its proximal end.
When the insertion tube of the borescope is inserted into a
borescope port of the gas turbine engine, the lens system at its
distal end relays an image of an otherwise inaccessible
intermediate compressor/turbine blade to the viewing means at the
proximal end. The focus of the image (in some models) can be
adjusted by control knobs at the proximal end of the borescope.
Hence, as illustrated by this example, a borescope permits an
intermediate compressor/turbine blade of a gas turbine engine to be
inspected without needing to disassemble the engine.
Besides being used to indirectly inspect parts which cannot be
inspected directly, borescopes can also be used to measure the size
of defects on the part. For example, U.S. Pat. No. 4,980,763
(hereinafter "the '763 patent") discusses a system for measuring
objects viewed through a borescope. The system discussed in the
'763 patent projects an auxiliary image, such as a shadow, onto the
object being viewed. Changes in the position or size of the
auxiliary image correspond to the distance between the object being
viewed and the borescope. The image is displayed on a monitor
having a magnification and object distance scale overlay on the
screen. The size of the object on the screen is measured with
vernier calipers, or electronically with cursors. This size is then
divided by the magnification which is determined by observing where
the auxiliary image falls on the magnification overlay.
Unfortunately, the system discussed in the '763 patent requires a
user to manually determine the magnification factor based on the
position of the auxiliary image on the display screen.
U.S. Pat. No. 4,207,594 (hereinafter "the '594 patent") discusses a
system in which the dimensions of a defect are determined based
upon a manually entered field-of-view value and a ratio of second
crosshairs, arranged at edges of a defect image, to first
crosshairs, arranged at edges of the field of view. Unfortunately,
the system discussed in the '594 patent requires probe penetration
values to be manually read from a scale on the probe barrel for
determining the field-of-view. Since such scales do not have fine
gradations and since they must be manually read, errors are
introduced.
U.S. Pat. No. 4,820,043 (hereinafter "the '043 patent") discusses a
technoscope for determining the length of a defect. The technoscope
includes a graduated scale which is displaceable in a direction
transverse to the endoscope axis. The graduated scale is
mechanically coupled with a detector which produces an electrical
signal based on the transverse displacement of the graduated scale.
The distance to the defect is determined by (i) observing the
object image at a first terminal position of a fixed stroke Z of
the endoscope, (ii) noting the intercept of the object image on the
graduated scale, (iii) axially displacing the endoscope by the
fixed stroke Z, and (iv) transversely displacing the graduated
scale until the defect image intercepts it at the same point as
before the axial displacement. A calculator uses the electrical
signal from the detector and a known focal length of endoscope to
determine the object distance. The size of the defect can be
similarly determined. The technoscope of the '043 patent also
includes a swing prism with a detector for determining its angular
position.
Unfortunately, the scope of the '043 patent requires that the focal
length of the endoscope be known ahead of time and requires two
measurements. Moreover, since the distance between the two
measurements must be fixed, the scope must be fixed with respect to
the object during the two measurements. Furthermore, limitations in
the gradations of the graduated scale limits the accuracy of the
readings. Also, by manually reading the intercept point of the
defect on the graduated scale, errors are introduced.
U.S. Pat. No. 4,702,229 (hereinafter "the '229 patent") discusses a
technoscope for measuring an object. The technoscope includes an
inner shaft which is axially displaceable with respect to an outer
shaft. A measuring scale is provided in the inner shaft. The
measurement of the object is determined by (i) placing an edge of
the object image on the measuring scale, (ii) fixing the
technoscope with respect to the object, (iii) axially displacing
the inner shaft by a fixed distance, and (iv) observing how many
scaler divisions the object image moved on the measurement scale.
The object size is determined based on a known system focal length,
the length of the displacement, and the number of scales moved by
the object. The '229 patent is similar to the '043 patent except
that with the '043 patent, the graduate scale is transversely
repositioned such that the object intercepts it at the same point
and the transverse position is determined with a mechanical
detector. Therefore, the device of the '229 patent suffers the same
drawbacks as the '043 patent, namely, (i) the focal length of the
technoscope must be known, (ii) two measurements are needed, during
which the technoscope must be fixed with respect to the object,
(iii) limitations in the gradations of the measurement scale
introduces errors, and (iv) the measurement scale must be manually
read.
Known devices also use a magnification scale ring arranged adjacent
to a focusing control ring having an indicator RV, for determining
the magnification of the scope. Based on the position of the
indicator of the focusing control ring with respect to the
magnification scale, the magnification of the scope at that object
distance is determined. Unfortunately, similar to the probe
penetration knob in the system discussed in the '594 patent, such
devices require magnification values to be manually read from a
scale on the magnification barrel. Since such scales do not have
fine gradations and since the magnification values must be manually
read, errors are introduced. Even if the scale had fine markings,
its diameter would have to be huge to have thousands of distinct
"markings."
When such a scope is equipped with a graticule and a diopter focus
control, this known device can also be used to determine the size
of a viewed object. A graticule is a scale etched into a surface of
a transparent glass plate included in the optical system. The
diopter focus control is used to focus the graticule scale. An
object is then focused by means of the focus control. Based on the
number of graticules covered by the object image and based on the
magnification level, the object size is determined. Unfortunately,
the graticule scale is manually read which introduces errors.
Manually reading the number of graticules covered by the object
image also fatigues the user's eye. Moreover, since the number of
markings on the graticule is limited, the accuracy is also limited.
Furthermore, this method is inaccurate because the eye will
accommodate an "out of focus" focus barrel position.
U.S. Pat. No. 4,558,691 (hereinafter "the '691 patent") discloses
an endoscope in which an actual size of an observed object, a
magnification of the scope, and an object distance can be
determined based on a positional relationship between an indicating
index and a stationary reference index. The indicating index is
formed on a glass plate which moves up and down, perpendicular to
the optical axis, as the lens barrel of the optical system moves
back and forth along the optical axis. Unfortunately, as with the
devices discussed above, the indicating index included in the
device described in the '691 patent does not have fine gradations
and must be manually read. This not only permits errors to be
introduced, but also fatigues the eye of a user.
Japanese Patent Publication No. 5-288988 (hereinafter "the '988
publication") discusses the use of an encoder for determining
changes in the magnification of a zoom lens system. However, this
system is to be used for viewing objects at a fixed distance. That
is, the encoder in the '988 publication determines changes in
magnification of the scope but cannot determine the initial
magnification of the scope and cannot determine object
distance.
In view of the above described problems with existing scope
measurement systems, a system for automatically measuring objects,
with high resolution, is needed.
SUMMARY OF THE INVENTION
The present invention fulfills the above mentioned need by
providing an arrangement including a scope having a focusing
mechanism to which a high resolution encoder is coupled. The
encoder sends a signal, corresponding to the position of the
focusing mechanism, to a processor. The image from the scope is
also sent to the processor. A processor executed program correlates
the encoder signal to object size and/or magnification.
The encoder may be either a relative encoder or an absolute
encoder, and may encode optically, electrically, and/or
magnetically. However, in a preferred embodiment of the system of
the present invention, the encoder is a relative, optical,
encoder.
In a first embodiment of the present invention, the scope is a
swing prism rigid borescope which allows the user to change the
scope's direction of view from the scope body. The encoder is
preferably a rotational optical encoder. The image from the scope
is preferably sent to the video processor via a camera mounted to
an eyepiece. In an embodiment of the system of the present
invention using a relational encoder, the relational encoder
increments and decrements an initial count based on adjustments of
the focusing device. The initial count is set when the focusing
device is placed in a predetermined home position.
In a second embodiment of the present invention, the scope is a
flexible focusing fiberscope having a focusing lens system at a
distal end and a focusing control at a proximal end. The focusing
control at the proximal end actuates at least one lens of the
focusing lens system at the distal end by means of a control cable
or by means of a fine pitch flexible screw. The encoder may be a
linear encoder located at the distal end for measuring the linear
movement of the at least one lens of the focusing lens system, or
it may be an encoder located at the proximal end for measuring a
movement of the focusing control. In a third embodiment, the scope
is a flexible video fiberscope having a focusing lens system at the
distal end and a focusing control at the proximal end.
Optical encoders may include rotational encoders or linear
encoders. The rotation encoders include an encoder disk, a light
source and a detection device. The encoder disk has apertures, or
reflective and non-reflective regions, arranged around its
circumference, and is mechanically coupled with the focusing device
such that it rotates when the focusing device is adjusted. The
light source directs light towards a first side of the encoder
disk. When an encoder disk having apertures is used, the detection
device is arranged on a second side of the encoder disk, and
generates a pulse when light from the light source passes through
an aperture of the encoder disk. On the other hand, if an encoder
disk with reflecting and non-reflecting regions is used, the
detection device is arranged on the first side of the encoder disk
and generates a pulse when light from the light source is reflected
by the encoder disk. A linear encoder is similar to the disk
encoder except it has a strip having a plurality of spaced
apertures or a plurality of reflecting and non-reflecting regions,
and is mechanically coupled with the focusing device such that it
is linearly translated when the focusing device is adjusted.
The present invention provides a system for determining a dimension
of a detail. The system at least includes an optical scope and a
processor, and may also include a video camera, a display device,
and a detail marking device. The optical scope produces an image of
the detail and includes a focusing device and an encoder.
Borescopes and fiberscopes also include a viewer. The focusing
device adjusts a focal position of the image of the detail. With
borescopes and fiberscopes, the viewer passes the image of the
detail to a plane outside of the optical scope. With videoscopes, a
video signal is provided. The encoder provides a focus position
signal based a position of the focusing device.
The video camera produces a video signal of the detail from the
image of the detail. In borescopes and fiberscopes, the video
camera is optically coupled with the viewer of the scope, while in
videoscopes, the video camera is internally mounted. The display
device displays the detail based on the video signal of the detail.
The detail marking device permits at least two markers, each having
a coordinate value, to be arranged on the display of the detail on
the display device. The processor converts the focus position
signal from the encoder into an object distance signal and then
into a magnification signal. The processor also determines the
dimension of the detail based on the coordinate values of the at
least two markers and based on the magnification signal.
In a preferred embodiment of the system of the present invention,
the optical scope is a swing prism rigid borescope. The optical
scope may also be a fiberscope or videoscope.
In a preferred embodiment of the system of the present invention,
the video camera includes a charge coupled device which converts
the image of the detail into the video signal of the detail.
Further, in the preferred embodiment of the system of the present
invention, the processor includes a first converter, such as a
formula or a look-up table, for converting the focus position
signal into an object distance signal, and a second converter, such
as a formula or look-up table, for converting the object distance
signal from the first converter into a magnification signal. In the
preferred embodiment, the processor also includes a size processor
for producing the dimension of the detail based on the
magnification signal from the second converter and based on the
coordinate values of the at least two markers.
In a preferred embodiment of the present invention, the optical
scope includes a distal lens system, a focusing lens, a focus
controller, and an encoder. If the optical scope is a borescope or
fiberscope, it also includes a viewer. The distal lens system
produces an image of a detail within its field-of-view. If the
optical scope is a borescope or fiberscope, the viewer passes an
image of the detail produced by the lens system to a plane outside
of the scope. The focusing lens is located between the distal lens
system and the viewer and can be linearly translated along its
optical axis thereby permitting a focal position of the image to be
adjusted. The focus controller linearly translates the focusing
lens along its optical axis, whereby different positions of the
focus controller correspond to different positions of the focusing
lens. If the optical scope is a videoscope, a video camera, such as
a CCD for example, converts an image to a video signal at the
distal end. The focusing control actuates at least one lens in a
lens system at the distal end. The encoder produces signals
corresponding to the different positions of the focusing lens being
translated or of the focus controller.
In an alternative embodiment of the present invention, the scope
automatically focuses the image onto the video camera. In this
embodiment, a stepper motor can actuate at least one lens of the
focusing lens system. Alternatively, a user may make processor
guided manual focusing adjustments. The user positions a cursor
upon the video image of the detail to be measured. Alternatively,
known methods of pattern detection could be used. A number of
samples of windows (i.e., a predetermined number of pixels around
the area of interest) are taken with the at least one lens of the
focusing lens system at different positions. The at least one lens
is translated by the stepper motor. The sampled window with the
maximum contrast, as determined by a known method, is considered to
be the most in focus. If there is more than one maximum contrast,
the processor can choose either (i) the near focus side position
having a maximum contrast, (ii) the far focus side position having
a maximum contrast, or (iii) the average focus position of the
maximum contrasts. This choice is predetermined. While any of the
three choices can be used, it must be used consistently and can be
the basis for system calibration.
In a preferred embodiment of the present invention, an optical
distortion, based on an eccentricity of the image with respect to
the focusing lens system, is corrected by the video processor. The
eccentricity is determined based on the location of the image on
the video camera and/or on the video monitor.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side view illustration of a rigid borescope.
FIG. 2 is an illustration of a marked focus barrel used in known
measuring scopes.
FIG. 3 is a cross-sectional side view of an ocular position
rotational encoder to be used with the system of the present
invention.
FIG. 4 is a plan view of the ocular position rotational encoder
shown in FIG. 3.
FIG. 5 is a perspective view illustrating a focus barrel having a
spiral groove.
FIG. 6 is a perspective view illustrating a borescope chassis
having a longitudinal slot.
FIGS. 7a and 7b are cross-sectional side views of the ocular
rotational encoder of FIG. 3 illustrating the difference in the
positions of the elements of the encoder when viewing relatively
distant objects and relatively close objects.
FIG. 8 is a schematic diagram of an emitter end plate, a code
wheel, and an encoder body of a rotational encoder that can be used
in the system of the present invention.
FIGS. 9a through 9d are timing diagrams of outputs of the
rotational encoder illustrated in FIG. 8.
FIG. 10 is a functional block diagram of the system of the present
invention.
FIG. 11 is a graph illustrating the relationship between
magnification and object distance for an exemplary borescope.
FIG. 12 is a look-up table for determining object distance from the
count produced by an exemplary encoder.
FIG. 13 is a flow diagram of a process for using the system of the
present invention.
FIG. 14a is a schematic illustrating an objective fiberscope having
a distally mounted encoder and having a proximal focusing cable to
mechanically link a focus control with a focusing lens system.
FIG. 14b is a schematic illustrating an objective fiberscope having
a distally mounted encoder and having a flexible fine pitch screw
and a fine pitch nut for mechanically linking a proximal focus
control with a focusing lens system.
FIG. 14c is an alternative embodiment of FIGS. 14a and 14b in which
a proximally mounted encoder is used instead of a distally mounted
encoder.
FIG. 15a is a schematic illustrating an objective videoscope having
a distally mounted encoder and having a focusing cable to
mechanically link a focus control with a proximal focusing lens
system.
FIG. 15b is a schematic illustrating an objective videoscope having
a distally mounted encoder and having a flexible fine pitch screw
and a fine pitch nut for mechanically linking a proximal focus
control with a focusing lens system.
FIG. 15c is an alternative embodiment of FIGS. 15a and 15b in which
a proximally mounted encoder is used instead of a distally mounted
encoder.
FIGS. 16a and 16b are video display screens for illustrating a
process for determining magnification and radial distortion
errors.
FIGS. 17 is a diagram which illustrates how magnifications are
determined.
FIG. 18 is a flowchart of an automatic focusing procedure of the
present invention.
FIG. 19 is a schematic diagram illustrating additional elements
used in an automatically focusing scope.
DETAILED DESCRIPTION
The following is a description of an exemplary embodiment of the
present invention which employs a rotational encoder with a
borescope. This example is not intended to limit the scope of the
invention to rigid borescopes or to rotational encoders. Instead,
the scope of the invention is defined by the claims which follow
the detailed description.
FIG. 1 is a side view illustration of a rigid borescope 1. The
borescope 1 includes a body 2 and a long, thin arm (or insertion
tube) 3. The insertion tube 3 is connected, at a proximal end, to
the body 2, has an insertion length WL, and includes a lens system
10 at its distal end. The lens system 10 has a field-of-view
defined by the angle FOV. As is illustrated in the partial side
views of the insertion tube 3, different lens systems 10a through
10d have different directions of view. The distal end of the
insertion tube 3 includes a cap 9 for protecting the insertion tube
3 from mechanical shocks resulting from inadvertent collisions. In
a preferred embodiment of the present invention, the rigid
borescope includes a swing prism, i.e., a prism which can be
pivoted. The direction of view of such a swing prism can be
adjusted from 45.degree. to 120.degree.. A sensor may be used to
determine the angular position of the prism. Any angular prism
position deviating from 90.degree. introduces optical errors. These
optical errors can be compensated for based on the sensor
output.
The body 2 of the borescope 1 includes an orbital scan control 8, a
focus control 4, a viewing means 11, and a light guide connector 6.
The orbital scan control 8 is used for rotating the insertion tube
3 for capturing different views. The angular orientation of the
insertion tube 3 is indicated with an orbital scan direction
indicator 7. The focus control 4 permits the image gathered by the
lens system 10 to be focused at the viewing means 11. The light
guide connection 6 permits a light source (not shown) to be coupled
with the borescope. The light from the light source may be carried
by a fiber optic bundle, for example, to the distal end of the
insertion tube 3 to illuminate objects within the field-of-view of
the lens system 10. The viewing means 11 provides the image
captured by the lens system 10. An eyecup 5 may be connected to the
viewing means 11 for direct viewing. Alternatively, as illustrated
in FIG. 10, a video camera 103 may be mounted to the viewing means
by means of a viewing means-to-camera adaptor 116. The video camera
103 may transmit a video signal to a video processor 108.
A "focusing borescope " is a borescope with adjustable focus which
produces a sharp image at a range of object distances. The narrow
field-of-view (e.g. FOV=20 degrees) results in a shallow
depth-of-field (DOF). As a consequence, with focusing borescopes,
positions of the focus barrel correspond to object distances.
Therefore, the focus barrel can be calibrated and used as a range
finder. Since the log of the scope magnification and the log of the
object distance have a linear relationship, the actual size of an
observed object can also be determined.
FIG. 2 is a marked focus barrel used in known measuring scopes,
such as a focusing borescope for example. Such a marked focus
barrel can be provided on the body 2 of the borescope 1 of FIG. 1
for example. The focus barrel of FIG. 2 includes a magnification
scale 22, a diopter focus control 23, a graticule orientation
control 24 and a focusing control 21 having an indicator 211. When
the observed image is focused, the position of the indicator 211 of
the focusing control 21 with respect to the magnification scale is
used to determine the magnification of the image. As mentioned
above, the log of the object distance is linearly related to the
log of the scope magnification. Therefore, once the magnification
of the image is determined, the object distance can be derived.
Furthermore, as discussed in the Background of the Invention above,
when the graticule (i.e., a scale etched into a surface of a
coverglass included in the optic system) is focused with the
diopter focus control 23, the size of the object being viewed can
be determined based on the number of graticules occupied by the
image of the object and based on the magnification of the
scope.
Unfortunately, a number of error sources are introduced when using
a scope with a marked focus barrel to determine the object
distance, i.e., as a range finder. First, the resolution of the
magnification value reading is limited by the gradations of the
magnification scale. Also, there is a very practical limit to the
number of graticule markings which limits the accuracy. Second, the
magnification scale 22 and the number of graticules covered by the
focused image must be manually read by a user. Third, manual
calculations and confusing multiple step procedures introduce the
possibility of human errors. Furthermore, the poor "ease of use "
of scope measuring systems employing marked focus barrels and the
experience of eye fatigue when using such scopes has limited their
acceptability. More importantly however, is that the eye will
accommodate slightly "out of focus" images. Furthermore,
differences in the eyesights of different users will lead to
different magnifications needed to focus the image. That is, users
having different eyesights will result it different focus positions
for the object being viewed.
FIG. 3 is a cross-sectional side view, and FIG. 4 is a partial plan
view, of an ocular position rotational encoder which can be used in
the scope measurement system of the present invention. The ocular
rotational encoder includes an encoder pickup 30 (described in more
detail with reference to FIG. 8), an encoder mounting plate 31, a
borescope chassis 32, an encoder disk 33, an encoder disk hub 34, a
carrier with an ocular lens 35, a ocular position pin 36, a viewing
means 37, a focusing knob 38, and a focusing barrel 39.
The ocular position rotational encoder can be mounted to a rigid
borescope by means of the mounting plate 31. The viewing means 37
is an eyepiece. However, as illustrated in FIG. 10, in the
preferred embodiment of the present invention, a video camera 103
is mounted to the viewing means 37 with a camera adaptor 116. The
video camera 103 transmits a video signal to a video processor 108
which displays the captured image 110 on a display monitor 109.
This arrangement permits the image captured to be more accurately
focused than would be possible with a human eye at the viewing
means 37 because the video camera 103 includes an imaging means,
such as a charge coupled device (CCD) 104, which is maintained at a
fixed distance from the viewing means 37. Accordingly, the video
camera 103 provides a "hard plane of focus" which is advantageous
when compared with the different focus positions resulting from
different users having different eyesights as discussed above and
resulting from the eye's ability to accommodate slightly
"out-of-focus" images.
When the focusing knob 38 is rotated about the optical axis, the
ocular lens carrier 35 moves up or down as indicated by the arrows.
By viewing the image on the display monitor, the focusing knob 38
can be used to precisely focus the image transmitted through the
ocular lens held in the carrier 35. This is done as follows.
The focusing knob 38 is mechanically coupled with the focusing
barrel 39. In a preferred embodiment of the present invention, the
focusing knob 38 is directly attached to the focusing barrel 39. As
shown in FIG. 5, the focusing barrel 39 is cylindrical and has a
spiral groove 51 cut into its inner surface. The ocular position
pin 36 fits into the spiral groove 51. The inner surface of the
focusing barrel 39 has a slightly larger diameter that the outer
surface of the borescope chassis 32 thereby permitting the focusing
barrel 39 to rotate about the borescope chassis 32. As shown in
FIG. 6, the borescope chassis 32 has a longitudinal slot 61 through
which the ocular position pin 36 projects. Accordingly, when the
focusing knob 38 is rotated, the directly connected focusing barrel
39 also rotates about the borescope chassis 32. The spiral groove
51 on the inside surface of the focusing barrel 39 causes the
ocular positioning pin 36 to ride up or down in the longitudinal
slot 61 of the borescope chassis 32. Since the ocular positioning
pin 36 is attached to the ocular lens carrier 35, the ocular lens
can be moved up and down by rotating the focusing knob 38.
FIGS. 7a and 7b illustrate the relative positions of the ocular
lens carrier 35 and of the ocular positioning pin 36 within the
groove 51 on the inside surface of the focusing barrel 39, for an
object relatively far from the borescope and for an object
relatively close to the borescope, respectively. As illustrated in
FIG. 7a, when the object distance is relatively large, the ocular
lens carrier 35 is positioned far from the viewing means 37 and the
ocular positioning pin 36 is located high in the spiral groove 51
on the inside surface of the focusing barrel 39. On the other hand,
as illustrated in FIG. 7b, when the object distance is relatively
small, the ocular lens carrier 35 is positioned close to the
viewing means 37 and the ocular positioning pin 36 is located low
in the spiral groove 51 on the inside surface of the focusing
barrel 39.
As illustrated in FIG. 3, the focusing barrel 39 is also
mechanically coupled with and preferably directly connected to, the
disk hub 34 of the encoder disk 33. In a preferred embodiment of
the present invention, as shown in FIG. 4, the encoder disk 33 has
a number of slots or holes 40 (only three of which are shown for
clarity) arranged around the encoder disk 33, spaced in equal
angular increments. The encoder pick up 30, described in detail
with reference to FIG. 8, determines the angular rotation of the
encoder disk 33 by counting pulses received at the pickup 30.
The optical encoder which produces pulses corresponding to changes
in the focal position, is a so-called "relational encoder". That
is, an initial condition (i.e., an initial count) must be
determined before the count is incremented or decremented. This
initial condition is determined by locating the focal position to a
predetermined "home" position for which the count is known or reset
by the electronics, typically to zero. The known or reset count is
then incremented and/or decremented when the focal position is
moved from the "home" position. The "home" focal position is
preferably located at at least one of the two extreme focal
positions. Alternatively, a home position can be determined with an
"indexing channel" as described below.
As an alternative to such "relational encoders," which increment
and/or decrement a known count when the focal position is moved
from a predetermined position, an "absolute encoder," which
includes information about its absolute angular (or linear)
position may be used.
FIG. 8 is a schematic diagram of the encoder optical pick-up 30.
The encoder optical pick-up 30 includes an emitter end plate 81
arranged adjacent to a first surface of the encoder disk 33 and an
encoder body 82 arranged adjacent to a second surface of the
encoder disk 33.
The encoder end plate 81 includes a series of light emitting diodes
83a through 83c for emitting light which is collimated by lenses
84a through 84c, respectively. These collimated light beams are
directed towards the first surface of the encoder disk 33.
The encoder body 82 includes a phase plate 85, lens pairs 86a
through 86c, and detection elements 87a through 87c for three (or
two in an alternative embodiment) channels. Each of the channels
87a through 87c includes an integrated circuit having two
photodiodes each having its own amplifier 88a through 88c. The
amplifiers 88a.sub.1 through 88c.sub.1 are electrically coupled
with a non-inverting input of comparators 89a through 89c,
respectively, while the amplifiers 88a.sub.2 through 88c.sub.2 are
electrically coupled with an inverting input of the comparators 89a
through 89c, respectively.
The collimated light beams from lenses 84a through 84c must pass
through a slit 40 in the encoder disk 33 and through an opening in
the phase plate 85 to reach lens pairs 86a through 86c,
respectively. The apertures in the phase plate 85 are positioned
such that, for each photo-diode/amplifier pair 88a through 88c, a
light period on one detector always corresponds to a dark period on
the other. Accordingly, the output state of the comparators 89a
through 89c changes when the difference of the two photo currents
produced by the photo-diode/amplifier pairs 88a through 88c,
respectively, changes sign.
The phase plate 85 is also arranged so that the channel 87a is 90
degrees out of phase (i.e., in quadrature) with the channel 87b as
is shown in the timing diagram of FIGS. 9a and 9b. This phase
difference permits the direction of rotation to be determined by
observing which channel is the leading waveform.
The channel 87c is an optional channel for performing an indexing
function. Specifically, the channel 87c generates an index pulse
for each rotation of the encoder wheel 33. This indexing channel
can be used to define a "home" focal position having a known count,
thereby providing an initial condition, i.e., an initial count, for
this "relational" encoder.
FIG. 10 is a functional block diagram of the system of the present
invention. An image captured by the borescope 1 is provided to a
video camera 103 which is coupled with the viewing means 37 of the
borescope 1 via a viewing means-to-camera adaptor 116. The video
camera 103 includes an imaging device 104, such as a charge-coupled
device (CCD) for example, for converting the optical signal to an
analog video signal. The analog video signal is supplied to a video
processor 108. The video processor 108 provides a video signal of
the object to a video display monitor 109 via a digital video frame
capturing device 115. The focusing knob 38 is adjusted until an
image of the object 110 being observed appears in focus on the
video display monitor 109. For objects oriented at an angle to the
plane of the optical system of the scope, multiple points or
regions of the object can be separately focused.
While the focusing knob 38 is being adjusted, the encoder 30
generates pulses corresponding to the angular rotation of the
focusing knob 38. The encoder 30 transmits the pulses of channels
87a, 87b, and 87c to a counter 101. The counter 101 increments or
decrements the count, depending upon whether the focusing knob 38
is being rotated clockwise or counter-clockwise, thereby forming a
digital count value. An initial count is generated when the focus
position is at "home" position as discussed above. The digital
count value is stored in a buffer 102.
When the object being observed 110 appears in focus on the video
display monitor 109, the user actuates a switch 112, such as a key
of a keypad, to "freeze" the image. When the switch 112 is
actuated, the digital count stored in the buffer 102 is read out
and provided as an input to a count-to-object distance converter
106, and the video frame stored in the digital video frame capture
115 is read out and provided to the video display monitor 109. If
multiple points or regions of an angled object are separately
focused as provided above, the counts corresponding to the separate
focus positions are averaged. In a further embodiment of the
present invention, described more fully below, multiple points of a
feature, such as a ding, can be separately focused and the measured
point distances used to determine the depth (or height) of the
feature or of parts of the feature.
The count-to-object distance converter 106 can be implemented as a
predetermined formula for converting the digital count to an object
distance. For example:
wherein
x=object distance
y=encoder count
a,b,c=constants
Alternatively, the object distance can be determined from the count
by means of a look up table including empirically determined data.
FIG. 12 shows an example of such a look up table. If a look up
table is used for converting the digital count to an object
distance, an interpolation routine is preferably also used for
determining object distances when the digital count falls between
count values listed in the look up table.
The object distance determined by the count-to-object distance
converter 106 is provided as an input to an object
distance-to-magnification converter 107. Similar to the
count-to-object distance converter 106, the object
distance-to-magnification converter 107 can be implemented as a
predetermined formula for converting the object distance to a
magnification value. Alternatively, the magnification value can be
determined from the object distance by means of a look up table and
an optional interpolator. As the graph shown in FIG. 11
illustrates, a linear relationship exists between the log of the
magnification and the log of the object distance.
The system of the present invention also can automatically
compensate for changes in the magnification from system to system
due to differences in the video cameras (such as CCDs for example)
and due to differences in the coupling between the eyepiece and the
video camera. This automatic compensation eliminates the need to
calibrate the magnification for each scope or system. The system of
the present invention can also compensate for optical distortions
due to image eccentricity. All optical systems distort. The main
component of optical distortion for scopes results from images that
do not pass through the center point of the lenses of the lens
system. Specifically, an optical distortion is a function of the
radial distance from the center of the lens to the point at which
the image passes, i.e., the optical distortion is greater when the
image passes through the edges of the lens than when the image
passes through the center of the lens.
The system of the present invention automatically compensates for
variations in magnification and for optical distortion as follows.
FIG. 16a illustrates a screen of the display 109 showing the image
of the defect 110. Since the actual image does not fill on the
entire area of an imaging device (such as a CCD 104 for example) of
the video camera 103, the scope image 161 does not fill the entire
screen of the display 109. The size of the scope image 161 depends,
at least in part, on the optical coupling of the image to the
imaging device. A user can move and adjust the diameter of the
circle 162 with an input device, such as the cursor input control
113, for example. The user moves and adjusts the circle 162 such
that it coincides with the scope image 161 on the display. (See
FIG. 16b). A processor, such as the size processor 114, compensates
the magnification of the optical scope 1--video camera 103
combination based on the diameter of the circle 162. FIG. 17 is a
diagram which illustrates the magnification compensation. Once the
object distance (OD) is determined, the actual size of the diameter
of the optical scope (D.sub.OS) can be determined since the field
of view (FOV=20) is known. Specifically D.sub.OS =2X=2
[OD(tan.theta.)]. The magnification is then determined based on the
ratio of the diameter of the circle 162 (when it coincides with the
scope image 161) over D.sub.OS.
FIG. 16a also illustrates a crosshair 164 which can be moved by a
user with an input device, such as the cursor input control 113. As
shown in FIG. 16b, the user can position the crosshair 164 at the
center of the scope image 161 so that an eccentricity "E" from the
center 165 of the display can be determined. A processor, such as
the size processor 114 for example, can compensate for optical
distortions based on the eccentricity "E".
The magnification compensation and the optical distortion
compensation may be separately provided. However, if both are
provided, the present invention preferably combines the crosshair
164 to coincide with the center of the circle 162 so that the image
size and eccentricity can be determined based on a single user
input. Alternatively, a processor executed program can determine
the size of the scope image 161 and the eccentricity "E"
automatically without requiring a user input. The optical scope may
also include a non-volatile memory for communicating stored
calibration information with other components of the system.
Referring back to FIG. 10, after a user actuates the freeze image
switch 112, the user manipulates a cursor control input device 113,
such as a keypad, a trackball, or a joystick, for example, to
position at least two crosshairs 111a and 111b at ends of the
object 110 being displayed. The coordinate positions of the
crosshairs 111a and 111b, as well as the magnification factor, are
provided as inputs to a size processor 114 which computes the
length or size of the object 110 being displayed. Alternatively, a
graticule (or reticle) provided in the optical scope can be used
for providing scaled image information to the user. This scaled
image information can be manually input into the size processor
114. Alternatively, a micro adjustable reticle can be used for
marking and can be coupled with an encoder for providing direct
inputs to the processor.
The display 109 can also optionally display the current object
distance. As will be described more fully below, displaying the
current, in-focus, object distance is useful for making depth and
height measurements.
It should be evident from the above description that various
combinations of the count-to-object distance converter 106, object
distance-to-magnification converter 107 and size processor 114 are
readily possible. For instance, the formulas or look up tables used
to implement the count-to-object distance converter 106 and the
object distance-to-magnification converter 107 can be implemented
with one formula or look up table which uses the focus count from
the buffer 102 as an input and provides the magnification value as
an output. Similarly, the object distance-to-magnification
converter 107 can be combined with the size processor 114 so that
the object distance value from the count-to-object distance
converter 106 can be used directly by the combined block (107/114)
in determining the size of the object 110.
Operating the system of the present invention is almost fool-proof.
Moreover, the system of the present invention reduces eye fatigue.
As illustrated in the flow diagram of FIG. 13, the user is only
required to execute three simple steps. First, the user must adjust
the focus until the image on the display screen is focused as shown
in step 131. Next, as shown in step 132, the user freezes the
focused image. Finally, the user positions first and second
crosshairs on the object being displayed as shown in step 133.
Moreover, in the automatically focusing system described below, the
user only has to perform step 133. Accordingly, a user is only
required to execute three (or one) simple steps. This eliminates
many errors that could otherwise be introduced by the user.
The above is an exemplary embodiment of the system of the present
invention. One skilled in the art can modify the particular
components suggested without departing from the scope of the
invention recited in the claims. For example, a linear optical
encoder for providing the position of the ocular positioning pin 36
can be used in place of the encoder disk 33 and its optical pickup
30. Such a linear encoder could be a plastic or metal strip, having
equally spaced slits on it, and being mechanically coupled with the
ocular positioning pin 36. An optical sensor can be used to count
light and dark regions as the plastic or metal strip is moved with
respect to it. Instead of slots, reflective and non-reflective
regions can be used.
Furthermore, an electrical sensor, such as a rheostat, for example,
or a magnetic sensor, such as a hall sensor for example, can be
used to determine the position of the ocular lens. However, optical
encoders are preferred because they provide high resolution in a
relatively small package.
Similarly, the focusing barrel 39 can be mechanically coupled to
the encoder disk hub 34 by gears instead of being directly
connected. Also, instead of providing an encoder disk 33 with slits
40, a reflective encoder disk with pits can be used. Similarly,
instead of incrementing and/or decrementing a count of slits (a
relational encoder), the encoder disk can include coded angular
position information (an absolute encoder).
A fiberscope or videoscope may also be used instead of a rigid
borescope. As shown in FIG. 14a, the fiberscope 140 includes a
flexible insertion tube 141 having a focusing lens system 142 at
its distal end. A coherent fiber bundle 143 carries the image to
the proximal end of the insertion tube where a lens system (not
shown) provides an image to a viewer. Alternatively, the focusing
lens system 142 can be provided at the proximal end of the coherent
fiber bundle 143. The proximal end of the fiberscope 140 includes a
scope body 144 with a focus controller 145. The focus controller
145 can linearly translate a lens of the focusing lens system 142
by means of a control cable 146 as shown in FIG. 14a or by means of
a fine pitch flexible screw 147 and nut 148 as shown in FIG. 14b.
In the alternative embodiment having the focusing lens system 142
at the proximal end of the coherent fiber bundle 143, the focus
controller 145 can be more directly coupled with the at least one
lens. As shown in FIG. 14c, the encoder 149 may be located at the
proximal end of the fiberscope 140 to encode the movement of the
focus controller 145. However, as shown in FIGS. 14a and 14b, the
encoder is preferably a linear encoder located at the distal end of
the fiberscope 140 to encode the linear movement of the lens.
Providing the encoder at the distal end eliminates mechanical
position errors due to flexing or stretching in the focusing
control cable 146 or backlash in the flexible screw 147.
As shown in FIGS. 15a and 15b, a videoscope 150 has a video camera
151, such as a CCD, adjacent to a focusing lens system 152 at the
distal end of a flexible insertion tube 153. The video camera 151
converts the image to a video signal which is carried to the
proximal end of the videoscope by means of a video signal cable
154. Accordingly, a viewer is not required in a videoscope.
As discussed above with reference to the fiberscope 140, a focus
controller 155, located at the proximal end of the videoscope 150,
can linearly translate a lens of the focusing lens system 152 by
means of a focusing control cable 156 (See FIG. 15a.) or by means
of a flexible screw 157 and nut 158 (See FIG. 15b.). Also, as
discussed above with reference to the fiberscope 140, the encoder
159 may be located at the proximal end of the videoscope to encode
the movement of the focus controller 155 (See FIG. 15c.) but is
preferably a linear encoder 159 located at the distal end of the
videoscope for encoding the linear movement of the lens (See FIGS.
15a and 15b.). In both the videoscope and fiberscope, if a
mechanical means is used to couple the focusing control with the at
least one lens, mechanical play in the mechanical means can be
compensated for by a processor.
If a fiberscope 140 is used, the system is similar to the system of
FIG. 10 which uses a borescope as the optical scope 1. However, if
a videoscope 150 is used, the viewing means-to-camera adaptor 116,
the externally mounted video camera 103 with CCD 104 are not needed
since the videoscope 150 includes an internal video camera such as
a CCD 151 for example.
In alternative embodiments of the scopes and systems of the present
invention, an automatic focusing device can be used in addition to,
or in place of, the focusing knob 38 of the borescope or the
focusing controls 145 and 155 of the fiberscope 140 and videoscope
150, respectively.
As shown in FIGS. 19a and 19b, a stepper motor 191 is mechanically
coupled with at least one lens of a focusing lens system 192, by
the means of a focus control cable or a fine pitch flexible screw
for example. An optional encoder 193 may also be mechanically
coupled with the stepper motor 191 (See FIG. 19a.) or with the at
least one lens of the focusing lens system 192 (See FIG. 19b.).
The object image is automatically focused with a processor 194
executed program. FIG. 18 is a flow chart illustrating the program
for automatic focus. At step 181, the user selects a point of
interest via an input device, such as the cursor input control 113
for example. Alternatively, the processor 194 can select a point of
interest using a known defect detection algorithm. Next, a window
is defined around the point of interest at step 182. The window may
be predetermined or may be defined by the user. The window is
preferably a rectangle but may be another geometric shape. For
example, the processor 194 can define a 10 pixel by 10 pixel box
centered around the point of interest. In a preferred embodiment,
the size of the window is limited decrease processing time.
In steps 183 and 184, the stepper motor is placed in an initial
position and the image within the window is sampled. In step 185,
the contrast of the sampled image is determined in a known way. For
example, the average of the magnitude of the differences in
brightness between adjacent pixels can be determined. The higher
the average, the higher the image contrast. Alternatively, a Fast
Fourier Transform (FFT) of the image can be determined. The higher
frequency, the more complex the image and the higher the
contrast.
Step 186 determines whether the contrast determined in Step 185 is
a maximum. Since the maximum contrast value corresponds to the
"best focus," a focus position value is related to the current
stepper motor position in step 187 when the contrast is a
maximum.
Steps 184 through 187 are repeated until a range of stepper motor
positions is complete, as illustrated by steps 188 and 189. If a
maximum contrast is determined at more than one stepper motor
position, the best focus is selected from either (i) a maximum
contrast position nearest to the focus size, (ii) a maximum
contrast position farthest from the focus side, or (iii) an average
of the maximum contrast positions. In an embodiment having
automatic focusing and a defect detection process, a display is not
required.
As can be inferred from FIG. 19a, it is possible to eliminate the
encoder 193 and base the focus position on the number of steps
executed by the stepper motor 191. This would be especially
practical if a small stepper motor could be arranged at the distal
end of the insertion tube. If however, the stepper motor 191 is
located at the proximal end of the scope as in FIG. 19b, an encoder
193 is preferably included at the distal end of the insertion tube
to eliminate any errors due to mechanical "play" in the mechanical
coupling between the stepper motor 191 and the at least one lens of
the focusing lens system 192. Alternatively, a user may make
processor guided manual adjustments.
In a preferred embodiment of the present invention, a focus knob
(or focusing controller) is used with the stepper motor in a
"hybrid" focusing operation. A user first uses the focusing knob to
coarsely focus the image. The stepper motor then performs a fine
image focus under control of the processor as described with
respect to FIG. 18. Such a "hybrid" operation is advantageous
because the range of stepper positions at which the image is to be
sampled and analyzed is decreased.
The system of the present invention can also be used to measure
depth and height by determining the difference between the measured
object distances of two points. For example, the depth of a
round-bottomed ding in the surface of a turbine blade can be
determined by 1) first focusing the device of the present invention
on the surface of the blade and determining the object distance, 2)
recording the measured object distance to the blade surface, 3)
focusing on the bottom of the ding and determining the object
distance, and 4) subtracting the recorded object distance to the
blade surface from the object distance to the ding bottom, thereby
yielding the depth of the ding.
The above-described procedure can be carried out manually using any
of the embodiments of the present invention described thus far. For
example, with the embodiment of FIG. 10, the user can note the
object distances displayed on the display 109 for the two points of
interest (i.e., the blade surface and the ding bottom) and subtract
the two quantities to determine the depth of the ding.
The system of the present invention can provide various features to
facilitate the depth/height measurement procedure. The embodiment
of FIG. 10, for example, can be adapted to provide such features by
modifying the software used to program the system. For example,
once the user causes the system to focus on the first point, e.g.,
the blade surface, and has hit image freeze switch 112, the object
distance, as determined by the count-to-object distance converter
106, is temporarily stored by the software in a register or memory
location (not shown). When the user causes the system to focus on
the second point, e.g., the ding bottom, and hits the image freeze
switch 112, the system will subtract the stored object distance
from the current object distance, as generated by the converter
106, and display the difference on the display 109.
Optionally, once the first point has been focused and measured, as
the system is being re-focused and before the freeze switch 112 is
pressed again, the system can display the current object distance,
the stored object distance of the previously frozen image, and/or
the difference between the two object distances. By updating and
displaying, in real time, the current object distance and/or the
difference between the current object distance and the stored
object distance, the user can search for the lowest point (or
highest point) of the feature whose depth (or height) is to be
determined.
The procedure for determining the depth or height of a feature can
be automated even further with the system of the present invention.
For example, in one embodiment, once the user has aimed the scope
at a feature whose depth or height is to be determined, the system
can then automatically carry out the depth/height measurement
procedure. Using the automatic focusing procedure described above,
the system can focus on and determine the object distance of each
of a predefined number of uniformly distributed points within a
window of a predefined size surrounding the feature. Once all
points within the window have been measured, the system then
determines the minimum and maximum values of the plurality of
object distances measured. The system then determines the
difference between the minimum and maximum object distance values,
which difference represents the depth or height of the feature.
It will be appreciated that when measuring the depth or height of a
feature relative to a surrounding flat surface, the scope should
preferably be oriented so that its optical axis is perpendicular to
the surface. If this, however, is not the case, at least three
points on the surface must be measured in order to identify the
plane of the surface. Once the plane has been identified, the
feature's depth or height relative to the plane can then be
determined. Such a procedure can be carried out, for instance, with
the embodiment of FIG. 10 with modified software. Using the cursor
control, the user can define three points in the plane surrounding
the feature of interest. The system of the present invention then
automatically focuses on and determines the object distance for
each of the three points. Using the cursor position information and
the object distance calculated for each point, the system thereby
has three-dimensional coordinates for each point. The system then
uses those coordinates to determine the plane of the surface
surrounding the feature of interest. When the user then positions
the cursor on the displayed image of the feature, the system
measures the object distance to the point defined by the cursor and
calculates and displays the depth or height of that point on the
feature relative to the plane surrounding the feature. The user can
then iteratively position the cursor on the displayed image of the
feature until he determines the maximum depth or height, or any
intermediate depth or height of interest. This procedure can also
be further automated, as discussed above, by programming the system
to automatically focus and measure multiple points in a window
surrounding a feature.
For applications which only call for the measurement of the depth
or height of features, as opposed to their width, a simplification
of the system of the present invention can be achieved by
eliminating the determination of the magnification. In this case,
only the object distance is required.
* * * * *